1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a fabrication method of an electron-beam (E-beam)/X-ray mask for a semiconductor device applying a lift-off method.
2. Discussion of the Related Art
FIGS. 1A-1E sequentially illustrate a conventional fabrication method of an X-ray mask for a semiconductor device.
In FIG. 1A, a thin film (not shown) is formed on a silicon wafer 1, and an absorbent film (metal) 2 is deposited on the wafer 1 including the thin film. The thin film is formed of Si, SiC, or SiN, etc., and the absorbent film 2 is formed of tungsten (W), gold (Au), or platinum (Pt), etc.
In FIG. 1B, a photoresist film 3 is applied and formed on the absorbent film 2.
Next, in FIG. 1C, the photoresist film 3 is patterned by a photo-etching process, thus forming a photoresist pattern 3a. In FIG. 1D, the absorbent film 2 is etched using the photoresist pattern 3a as a mask, thus forming an absorbent film pattern 2a on the wafer 1.
In FIG. 1E, the photoresist pattern 3a is removed, whereby the conventional mask for the semiconductor device is achieved. Next, a back side Si etch is performed, thus obtaining the conventional X-ray mask for the semiconductor device.
FIGS. 2A-2D sequentially illustrate a fabrication method of a conventional E-beam/X-ray mask for a semiconductor device applying the lift-off method.
In FIGS. 2A and 2B, a photoresist film 3 is applied on a silicon wafer 1, and patterned by the photo-etching process, thus forming a photoresist pattern 3a.
In FIG. 2C, a metal 2 is formed on the silicon wafer 1 and the photoresist pattern 3a. The metal 2 is physically deposited thereon by one of sputtering, evaporation, or ion clustering.
Next, as shown in FIG. 2D, a photoresist etching solution is used to remove the photoresist pattern 3a and a part of the metal 2 which is formed thereon. The part of the metal 2 which is formed on the silicon wafer 1 therefore remains, thus obtaining the conventional E-beam/X-ray mask for the semiconductor device using the lift-off method.
When manufacturing the conventional X-ray mask for the semiconductor device, a metal etching process is required for forming a metal pattern on a silicon wafer. When a thick metal layer is formed, it is difficult to etch the metal layer, and, particularly, it is hard to carry out an anisotropic etching process when forming a metal pattern, such as platinum, which seems to have difficulty in a dry-etching process. Also, according to the fabrication method of the conventional mask for a semiconductor device by the lift-off method, when step coverage is uniform so that a metal layer is formed on a sidewall of a photoresist pattern, it is hard to remove the metal layer formed on an upper surface of the photoresist pattern.